Ultrashallow Junction Electrodes in Low-Loss Silicon Microring Resonators

Bin-Bin Xu, Gabriele G. de Boo, Brett C. Johnson, Miloš Rančić, Alvaro Casas Bedoya, Blair Morrison, Jeffrey C. McCallum, Benjamin J. Eggleton, Matthew J. Sellars, Chunming Yin, and Sven Rogge

Phys. Rev. Applied 15, 044014 – Published 7 April 2021

Abstract

Electrodes in close proximity to an active area of a device are required for sufficient electrical control. The integration of such electrodes into optical devices can be challenging since low optical losses must be retained to realize high-quality operation. Here, we demonstrate that it is possible to place a metallic shallow phosphorus doped layer in a silicon microring cavity that can function at cryogenic temperatures. We verify that the shallow doping layer affects the local refractive index while inducing minimal losses with quality factors up to $10^{5}$ . This demonstration opens up a pathway to the integration of an electronic device, such as a single-electron transistor, into an optical circuit on the same material platform.

Received 11 October 2020
Revised 18 January 2021
Accepted 10 March 2021

DOI:https://doi.org/10.1103/PhysRevApplied.15.044014

Physics Subject Headings (PhySH)

Electrical conductivity Integrated optics Nanophotonics Optoelectronics

Devices Junctions Semiconductor microcavities

Cavity resonators

Atomic, Molecular & OpticalCondensed Matter, Materials & Applied Physics

Authors & Affiliations

Bin-Bin Xu¹, Gabriele G. de Boo ¹, Brett C. Johnson^2,3, Miloš Rančić⁴, Alvaro Casas Bedoya ^5,6, Blair Morrison^5,6, Jeffrey C. McCallum², Benjamin J. Eggleton^5,6, Matthew J. Sellars⁴, Chunming Yin ^1,7,*, and Sven Rogge¹

¹Centre of Excellence for Quantum Computation and Communication Technology, School of Physics, University of New South Wales, Sydney, NSW 2052, Australia
²Centre of Excellence for Quantum Computation and Communication Technology, School of Physics, University of Melbourne, Parkville, Victoria 3010, Australia
³Centre of Excellence for Quantum Computation and Communication Technology, School of Engineering, RMIT University, Melbourne, Victoria 3001, Australia
⁴Centre of Excellence for Quantum Computation and Communication Technology, Research School of Physics and Engineering, Australian National University, ACT, Canberra 0200, Australia
⁵Institute of Photonics and Optical Science (IPOS), School of Physics, The University of Sydney, Camperdown, NSW 2006, Australia
⁶The University of Sydney Nano Institute (Sydney Nano), The University of Sydney, Camperdown, NSW 2006, Australia
⁷CAS Key Laboratory of Microscale Magnetic Resonance and Department of Modern Physics, University of Science and Technology of China, Hefei 230026, China

^*c.yin@unsw.edu.au

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Vol. 15, Iss. 4 — April 2021

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Images

Figure 1
(a) A conceptual schematic of the device, which consists of a $Si$ ring resonator and integrated cryogenic compatible electrodes for qubit readout. The qubit is represented by the red dot between the electrodes within the $Si$ ring. The light field is projected onto the $Si$ for illustration purposes only. (b) A cross section of the ring showing the profile of the electrode. (c) A Monte Carlo simulation of the implanted 4-keV $P$ profile. In this example, the implantation fluence is $1.3 \times 10^{14} {cm}^{- 2}$ , resulting in a peak $P$ concentration of $1.1 \times 10^{20} {cm}^{- 3}$ . The expected $P$ concentration after annealing for 15 s at $900^{\circ} C$ is also shown.
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Figure 2
(a) Simulation of the electric field for a TE mode at a wavelength of 1550 nm inside a waveguide with a $220 \times 450 {nm}^{2}$ cross-section area. The scale bar is $0.2 μ m$ . (b) The electric field profile through the waveguide determined at the dashed line in (a). This is shown for top layers with $k_{d} = 0$ and $k_{d} = 5$ . (c) The effective refractive indices $n_{eff}$ and $i k_{eff}$ for different $k_{d}$ values and different doped-layer thicknesses. The dashed line and the colored lines are plotted against the left and right axes, respectively. (d) The corresponding loss calculated from the $k_{eff}$ values in (c). Two experimental values for the loss (symbols) are also included, as discussed in the text.
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Figure 3
(a) Transmission spectra for a 20- $μ m$ -diameter ring cavity, measured before implantation, after implantation, and after postimplantation annealing. The spectra are offset vertically by $- 10$ dB for clarity. (b) An enlargement of the region indicated by the box in (a). These spectra are shifted by 1554.78, 1553.15, and 1551.65 nm, respectively. The solid lines are Lorentzian fits. The split resonance is fitted with two independent Lorentzians.
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Figure 4
(a) A false-colored SEM micrograph of a $34.3$ - $μ m$ -diameter microring cavity doped in an area of $200 \times 450 {nm}^{2}$ . The $P$ -implant window in the top-right region is colored in red. (b) Spectra of device 1 initially, after implantation and after the implantation and annealing processing steps. The spectra are offset vertically by $- 20$ dB for clarity. (c) An enlargement of the resonant peaks around 1535.5 nm indicated by the box in (a). These spectra are shifted by 1535.59, 1536.15, and 1536.26 nm, respectively and fit with Lorentzians. Although resolved mode splitting cannot be observed, a function consisting of two Lorentzians provides a better fit to the implanted and annealed device resonance in this case.
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Figure 5
(a) The $Q$ factor for device 1, determined from the resonant peaks before implantation, after local (not full) implantation, and after annealing. (b) A box plot of the $Q$ -factor distributions of all resonant peaks shown in (a) together with those of nominally similar devices within the 1530–1570-nm wavelength range. The vertical bounds of the boxes denote the standard deviation and the vertical lines the minimum and maximum values. The mean value of the $Q$ factor is shown as a horizontal line across each box. The cavities of the three devices have the same diameter of $34.3 μ m$ , with an air gap of $150 \pm 10$ nm.
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Figure 6
(a) A false-colored SEM micrograph of a 14- $μ m$ -diameter ring-resonator device with a $P$ -doped section (colored in red) between the $Al$ contacts (uncolored). (b) The $I$ - $V$ traces measured at room temperature and at 4.2 K showing Ohmic behavior as inferred by the linear fit.
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